<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title></title>
    <script>
    let arr=[12,5,88,37,21,91,17,24];

    let sum=arr.reduce((tmp,item,index)=>{
      return tmp+item;
    });

    console.log(sum/arr.length);
    </script>
  </head>
  <body>

  </body>
</html>
